Jamieson, Fausset and Brown on Psalms 106:24-27

24-27. The sin of refusing to invade Canaan, "the pleasant land" (Jr 3:19; Eze 20:6; Da 8:9), "the land of beauty," was punished by the destruction of that generation (Nu 14:28), and the threat of dispersion (De 4:25; 28:32) afterwards made to their posterity, and fulfilled in the great calamities now bewailed, may have also been then added.

despised--(Nu 14:31).

believed not his word--by which He promised He would give them the land; but rather the word of the faithless spies (compare Psa 78:22).